Does anyone know what it could be?

C1241 is not a real problem. But your hybrid battery meter going from full to empty really quick is a problem with the hybrid battery getting really weak. So it might be time to recondition the battery or change it for a new one.

 

I'm not sure what isn't 'real' about C1241. It's a problem with 12-volt power reaching the brake ECU. Sometimes it affects only the brake ECU (say, a damaged power wire serving the ECU), and sometimes it hints at a problem affecting multiple systems (say, very low voltage from the 12-volt battery).

C1310 is a code that isn't for a real brake problem: it is reported by the brake ECU, but it is set because the hybrid-vehicle control ECU has a problem to report and the brake ECU heard about it. The best way to get the full story is to use a scan tool that is able to get the trouble code(s) from the HV control ECU.

 

Go play with your 12 volt system Make sure you're 12 volt actually has 12 volts with some juice behind it to back it up The AH part of the battery we're talking the 12 volt here no 12 volts lots of lights lots of communication problems lots of funny business intermittent 12 volts same thing an AGM battery that's worth it salt is going to be generally showing 12.3 to 12.7 volts at rest You get lower than that and you are way off and things will stop communicating and communicator radically and screw up the can bus so maybe not have that going on once that is established and cleared then you can move forward with a tweaky 12 volt system You're never going to get much of anywhere.

 

It is sometimes corrosion at the ecu connection, and yes, the hybrid battery is going south